50V on a CATV.

[strmtrpr73]

Quick question, I was on a service call the other day, and the homeowner stated that the CATV installer said that the CATV lines from in the house had 50V on them at his splitter. SO I checked it out. Now I disconnected his CATV wire and took a reading, and I found 50V. I also noticed that his splitter wasn't wasn't?grounded, So I grounded it. Which fixed it at the main line coming to the splitter(which has a grounded coupling on it.) Before I did this I checked out the house. I disconnected all the TVs , and What do you think happened. NO voltage.
Now My question is, How can the CATV company tell the homeowner that the electrical system isn't properly grounded, and is causing his equipment to fail? The 50V is common coming from a TV, I have tested several since then, or Maybe all the other systems that I have tested are wrong too, and the homeowners are just lucky that their equipment hasn't failed. Any comments?

 

[hurk27]

Re: 50V on a CATV.

This is when a reverse polarity connection happens at a receptacle or in the power cord of a TV the chassie of a TV is not isolated from the neutral as one might think and presents a very big problem when somone changes the power cord to the back of the set. there are resistors and caps that connect between the chassie ground and the neutral in the power cord. this will apply a voltage to the coax when the polartiy is switched so this would be the first thing to look for. Check with a voltage meter (after all other TV's are disconect from the cable) each TV from a metal point on the set to the neutral untill you find the one that has the voltage then check to see if the cord is reversed or the receptacle is.

 

[hbiss]

Re: 50V on a CATV.

...the CATV installer said that the CATV lines from in the house had 50V on them at his splitter.

If the splitter and coax were properly bonded to ground at the service entrance LIKE THE CATV COMPANY IS SUPPOSED TO DO there wouldn't be any voltage to measure.

Now My question is, How can the CATV company tell the homeowner that the electrical system isn't properly grounded, and is causing his equipment to fail?

Because they are brain dead! Read what I just said above!

I also agree that any voltage on the coax connector to ground on a TV is caused by a problem with the TV and is definitely abnormal and a hazard.

 

[satman]

Re: 50V on a CATV.

Measuring AC voltage from a TV to a good ground can be misleading.

The Volt meter is a high impedance measuring device. To correctly measure the voltage difference between a TV and the grounded cable, one must use a 1500 ohm 10 watt resistor in parallel with a 0.15mfd ac type capacitor.
A measurement in excess of 0.75Vrms (0.5ma AC) is considered a potential shock hazard and must be corrected immediately.

Be safe
satman

 

[hbiss]

Re: 50V on a CATV.

Yes, and that's a point that should be made here also.

 

[humble]

Re: 50V on a CATV.

Unbelievable!

Now I know why boats at the marina corrode away
through the cable television!
There have been reports of this for a long time and I repaired televisions years ago but never made the connection. We can do something about this.

Humble

 

[humble]

Re: 50V on a CATV.

I just remebered seeing the tag inside televisions years ago that stated that the chassis was hot!

Used to have customers call me and say that the TV bit them so bad that they fell down!

Do not touch the inside of your television unless you know what you are doing. The 26KV inside is more voltage than Amperes but you can sure get knocked a good one from it.
Humble

 

[hurk27]

Re: 50V on a CATV.

Yes you can get a 75 ohm 1 to 1 Isolator transformer to isolate the cable at the on shore declamation point. sometimes you can get the cable company to install one but not always.

 

[humble]

Re: 50V on a CATV.

Thanks for the tip

Humble

 

[jimwalker]

Re: 50V on a CATV.

Humble i too fixed TV from 1968 to mid 80's sometimes wonder if it was smart move to get out of it.They did have polarity plugs that better not be reversed.Getting hit with 40kv usually woke you up real fast.

 

[hurk27]

Re: 50V on a CATV.

Jim even if the cord was reversed you would not get 40kv on the chasie. but you would get 120 volts to any grounded metal close by. we use to refer this as a hot chasie. and not to uncommon as somone removing the interlock clip that held the cord in the set back would very easly install it back reversed. with cable being bonded at the pole the resistance drop would allow for a voltage to even be on the cable to a point on it's way to the pole. One thing it would do is it would burn out the X-ray protection that caused the voltage in the first place. this was a L/C circuit made up with resistors and capactors installed around the chasie to the neutral in the cord. If the cord was reversed and the chasie was grounded through the cable or a grounded anntena it would place this L/C circuit accross 120 volts and would burn the resistors out leaving only the cap's left. These cap's that are still left would place about 50 volts depending on the loading of the meter giving the reading. Most newer TV's have a isolated shilding employed now and it's now built in the CRT. and is not dependent on the chasie grounding.

And yes me too had to give up the TV repair service as the newer equipment with micro-electronic's required differant testing and componit replacment equipment that was very costly.

 

[humble]

Re: 50V on a CATV.

I miss the TV days.
Using the Degaussing coil was great fun for me at 15 was a whoot! I always had trouble with the concergance though. But my favorite were the RCA's with removable boards. you know, It used to be that if you just replaced a transister you could fix any set. I fixed countless televisions just by replacing either the horizontal output regulator and cleaning around the HV anode whether it be dust or tar from smoke. Or replacing the vertical/retrace transisters together. The old man that got me into it is gone now but he Liberated some concentration camp people and one of the men invented the beltron for restoring picture tubes. You know, He had a new beltron every year for free the last few years he was alive? He had not seen the man in over 60 years. I used the old rubber hose to knock things clean myself. That could fix alot of televisions as well. A few good licks on the picture tube stem
Humble